The present invention relates to a digital-analog (D-A) converter circuit formed in a semiconductor integrated circuit, and more particularly, relates to a composite D-A converter circuit including a resistance string D-A converter circuit unit and an Rxe2x88x922R ladder resistance D-A converter circuit unit.
The documents of the related art disclosing a conventional D-A converter circuit include Japanese Laid-Open Publication Nos. 62-227224 (Laid-Open Publication Date: Oct. 6, 1987), 5-206858 (Laid-Open Publication Date: Aug. 13, 1993), 8-46515 (Laid-Open Publication Date: Feb. 16, 1996) and 9-64744 (Laid-Open Publication Date: Mar. 7, 1997), and U.S. Pat. No. 4,338,591 (Issue Date: Jul. 6, 1982) and U.S. Pat. No. 4,491,825 (Issue Date: Jan. 1, 1985).
A D-A converter circuit is generally used to convert a digital input code to an analog quantity. The D-A converter circuits for integration primarily include a resistance string D-A converter circuit and an Rxe2x88x922R ladder resistance DA converter circuit. The resistance string D-A converter circuit is advantageous in terms of monotonicity, but the use of the resistance string D-A converter circuit is difficult from the standpoint of the pattern area and conversion accuracy when a digital input code has a large number of bits n. On the other hand, the use of the Rxe2x88x922R ladder resistance D-A converter circuit is difficult from the standpoint of the monotonicity and pattern area when a digital input code has a large number of bits n.
For example, in applications of the D-A converter circuit to a tester for testing another semiconductor device, there are strong requirements for the D-A converter circuit, including not only high conversion accuracy but also minimized pattern area for a single D-A converter circuit since a plurality of D-A converter circuits are integrated. Recently, multi-bit D-A conversion for converting a large number of bits is also strongly required. Any type of D-A converter circuit is effective in converting a small number of bits. However, difficulty in realizing high-precision conversion and increase in pattern area are problematic to configure a D-A converter circuit for converting a large number of bits.
As described above, it has been difficult to use the conventional resistance string or Rxe2x88x922R ladder resistance D-A converter circuit to convert a large number of bits.
It is an object of the present invention to provide a D-A converter circuit capable of accurately outputting, even when converting a large number of bits, a desired analog voltage without requiring device accuracy, and also capable of being integrated with a small pattern area.
In order to achieve this object, the D-A converter circuit of the present invention includes: a high-order D-A converter circuit unit for: receiving a high-order i bit signal (i less than n) of an n-bit digital input code, and outputting first and second voltages resulting from D-A conversion of the high-order i bit signal to first and second output nodes through first and second buffers, respectively; a low-order D-A converter circuit unit for receiving the first and second output node voltages of the high-order D-A converter circuit unit as reference voltages of an Rxe2x88x922R ladder circuit, and conducting D-A conversion of remaining low-order j bits (j less than n, j=nxe2x88x92i) of the n-bit digital input code for output to a third output node; a sample-and-hold unit for selectively sampling and holding the voltage on the third output node, i.e., the D-A conversion output of the n-bit digital input code, according to a value of the n-bit digital input code; and an output unit for multiplying the sampled and held D-A conversion output voltage by a gain with respect to an arbitrary central voltage.